The invention relates to a process for producing a sheetlike formulation comprising at least one single-layer active substance matrix for the controlled release of active substance to the vicinity of the application site, the active substances being selected from crop protection agents, biocides, fertilizers, plant strengtheners, cosmetic active principles and fragrances.
Formulations, whose preparation is described below, are known from many areas of life for which the time- and quantity-controlled release of one or more active substances is required. Depending on the area of use, these formulations are applied in the form of sheetlike structures such as labels, strips, pouches, plasters or plaques to certain substrates or objects from which they develop their action. Typical fields of use for such products that may be mentioned here include, for example, pest control, for example, in vineyards or in forestry, or for crop protection, perfumery and cosmetology.
For reasons of cost, such formulations are wherever possible formulated so that the active substance is contained in a flat, single-layer polymer film from which in the course of the use the active substance is released to the site or the vicinity of application. In general, these formulations have a layered structure, comprising at least one matrix layer containing active substance and at least one support layer in contact with the matrix layer. These layers can be present in a xe2x80x9csandwich-likexe2x80x9d form or are joined to one another at the sides and formed in the manner of a pouch. Depending on the field of use, they are usually also in fixed or detachable combination with different functional layers such as, for example, control membranes or protective layers.
Processes for producing formulations of the type specified are known. A common feature of such preparation processes known from practice is that the formulation is first of all produced in the form of a strip-shaped web embracing the active substance matrix, then combined, if desired, with other layers, and separated into sections of a desired size by punching or cutting.
Because of the diversity of active substances applicable by means of these devices, and because of the different physicochemical properties of these active substances, the preparation of the single-layer active substance matrix represents the central step in such processes. Among the prior art processes for the preparation of such formulations, the dissolving or dispersing of the active substances in matrix material, usually a polymer solution or polymer melt, with subsequent drying, is probably the process of choice for the person skilled in the art. However, not all active substances can be processed in this way. The processing of volatile active substances proves to be particularly problematic, since the evaporation of the active substance during the preparation is almost impossible to control. And temperature-sensitive, so-called thermally labile active substances can be used only with restrictions, if at all, for systems requiring heat treatment during the manufacturing process.
For this reason, a variety of solutions have been worked out over the course of time to allow the preparation of the releasing matrices, especially for volatile and/or thermally labile active substances. For example, the principle of a depot is used, in which problematic active substances are introduced into a multi-part product in the form of a discrete reservoir of active substance without thermal stressxe2x80x94for example, in a separate process step during preparation. Processes of this kind in which the preparation of matrix layers free from active substance and the introduction of the active substance into the product take place as temporally and spatially separate operating steps are known from the manufacture of numerous products but are very labour-intensive.
In accordance with the prior art, active substance can be incorporated into a matrix using a variety of techniques. For instance, the introduction of a flowable active substance medium under pressure, in addition to the pressurized insertion of a solid active substance body, and injection, belongs to known processes of incorporating active substance into solid matrices. The processes mentioned have the common feature that active substance is applied initially to a support on which it remains only temporarily, since it migrates into the matrix layers that are in contact with it. Constituents which prevent unwanted flow or escape and whose function is to halt the active substance temporarily are referred to in the technical literature using terms such as, for example, adsorption layer, active substance dispenser, active substance support, fixing aid, support material, and interlayer. Liquid-absorbing substrates suitable for this purpose include nonwoven, foam, paper or woven textile material.
In practice, however, known production processes are frequently associated with disadvantages, a selection of which is specified below, and, as a result, prove to be correspondingly complex:
The absorption capacity for liquid media is generally limited to a certain level, which is frequently a limiting factor in loading the matrix with active substance.
In order to obtain controlled, continuous release of active substance over prolonged periods of application and to rule out the possibility of unwanted side-effects caused by excessive release rates, an additional control layer is often necessary.
The use of additional materials prolongs production and complicates it technically, since the individual layers and elements must first be manufactured separately from one another and then combined with one another in one or more subsequent steps.
The use of additional elements may also impair the performance qualities of the product, especially the shear stability, since the incorporation of an active substance fixing means reduces the contact area between matrix layers which are to be united. In order to ensure, despite this, the desired structural integrity of the formulation, there is often a need for additional connecting areas, in the form, for example, of a peripheral adhesive edge, which result in an unwanted increase in the dimensions.
The embedding of additional support materials may, furthermore, adversely affect the flexibility and functionality of the product. This is particularly so if thicker layers are necessary as a result of a low absorptive capacity, e.g. the absorbency of the material. These disadvantages are extremely undesirable especially in the case of active substance patches applied to surfaces of plants.
The morphology of the higher plants, especially the low radius of curvature and the lack of evenness and cleanliness of surfaces of plants, indeed, imposes particularly stringent requirements on the flexibility and small dimensioning of such active substance formulations. Added to this are the severe conditions borne by the surfaces of plants as a result of natural weather conditions at the site of application, which increases their susceptibility to a possible loss of cohesion.
Because of the disadvantages described above, multilayer or multipart formulations cannot be used for a number of applications on account, firstly, of their functionality. Secondly, the production costs resulting from the relatively high level of expenditure of material and manufacture limit the marketability and acceptance of such products. For price-sensitive markets and those where competition is intense, in particular, it would be desirable to be able to offer inexpensive products of comparatively simple construction for temperature-sensitive and volatile active substances as well.
The object of the invention is therefore to provide a process for producing sheetlike active substance formulations comprising a single-layer matrix, containing active substance, for the controllable release of active substances, including volatile and temperature-sensitive substances, which avoids the disadvantages of the processes known from the prior art.
This object is achieved in accordance with the invention by means of a production process utilizing process steps described in detail below.
A process is proposed in which the single-layer active substance matrix of the device is produced using at least two layers, identical in composition, of a base material in the following component steps which are separated from one another temporally and spatially (ref rence numerals in accordance with FIG. 1):
a) provision of two prefabricable layers (1, 2), identical in composition, of a base material,
b) application of active substance to at least one of the two layers (1, 2),
c) placement of the two layers (1, 2) atop one another so as to enclose the active substance applied, and irreversible joining under pressure to form a laminate,
d) storage of the laminate for predeterminable duration under defined conditions, with migration of the active substance into the base layers (1, 2), and connection at their interfaces to form a homogenous matrix featuring substantially uniform dispensation of active substance.
Active substances incorporated by this process into the matrix of the formulation include, for example, crop protection agents, biocides, fertilizers, plant strengtheners, cosmetic active principles and fragrances. The matrix layers can comprise one or more active substances.
xe2x80x9cBiocidesxe2x80x9d, according to the EC Biocides Directive, which has been in force since 14 May 1998, are substances or formulations which as intended possess the capacity to kill living organisms or at least to restrict them in their vital function. They are used, inter alia, as wood preservatives, disinfectants, process preservatives, insecticides and rodenticides. The term xe2x80x9ccrop protection agentsxe2x80x9d, which in the present specification is used synonymously with xe2x80x9cpesticidesxe2x80x9d, and also the term xe2x80x9cplant strengthenersxe2x80x9d, are defined in xc2xa72 of the Crop Protection Act applying in Germany.
The term xe2x80x9cvolatile substancesxe2x80x9d refers to substances having an effective vapour pressure even at room temperature. Examples that may be mentioned include insecticidal compounds such as dimethoate and acephate or insect pheromones such as Z,E-9,1.2-tetradecadienol and Z,E-9,12-tetradecadien-1-yl acetate.
For the purposes of the present invention, the term xe2x80x9ctemperature-sensitivexe2x80x9d or xe2x80x9cthermally labilexe2x80x9d substances refers to substances which decompose, or whose biological activity is impaired, at a temperature xe2x89xa750xc2x0 C.
In the process of the invention, the single-layer active substance matrix comes about through direct introduction of active substance between identical matrix layers, which are subsequently united by pressure and stored for the purpose of xe2x80x9cmaturationxe2x80x9d. The principal advantage of this process lies in its avoidance of the use of additional active substance fixing aids, thereby considerably reducing the expenditure on material and manufacture and at the same time significantly improving the functional quality of the products produced in this way. As a manufacturing process which proceeds at room temperature, this process is of particular value for the production of devices comprising volatile and thermally labile substances.
Advantageous embodiments of the process according to the main claim can be inferred by the person skilled in the art from the features of the subclaims. They relate, for example, to volumetric metering of the active substance, the operating pressure required when active substance is admitted into the matrix layer, further process parameters associated with the xe2x80x9cmaturationxe2x80x9d of the matrix, the way in which the active substance is introduced and applied, the material basis of the matrix base material, particular properties of the active substance, and its designations.